The invention relates to a method for cold gas spraying, in which a spray powder containing photocatalytically active spray particles is accelerated in a nozzle by means of a carrier gas and forms a coating upon impact with a substrate. The invention further relates to coatings and objects with the coating.
In cold gas spraying methods, metallic spray particles are typically accelerated to high speeds in a relatively cold gas flow, a carrier gas, so that they form a coating upon striking a substrate or work piece because the particles are plastically deformed upon impact. In order to ensure that a coating is formed, the particles must be travelling at a minimum speed upon impact. The carrier gas and particles are generally accelerated in a Laval nozzle. The carrier gas is often heated, because the particles become ductile in the hot carrier gas, which favours coating formation upon impact. In addition, higher carrier gas velocities are achieved. However, it is important to ensure that the spray particles do not begin to melt. The temperature of the carrier gas is therefore relatively low, and consequently the procedure is called cold gas spraying or kinetic spraying.
There are various methods for producing photocatalytically active coatings. Such coatings have a catalytic effect when exposed to incident light. This is demonstrated for example in an anti-bacterial or anti-viral effect or also the initiation of redox reactions. Thus, disinfection and cleaning are possible in which pollutants are removed and bacteria and viruses eliminated. By doping the titanium dioxide, for example, it is possible to achieve an effect according to which a titanium dioxide coating that is normally photocatalytically active in UV light also becomes active in visible light.
European Patent EP 2 302 099 describes procedure for coating objects associated with sanitation, cooking or medicine by cold spraying with photocatalytically active titanium dioxide. European Patent EP 1 785 508 discloses cold gas spraying of photocatalytically active titanium dioxide, wherein the spraying powder consists of photocatalytically active titanium dioxide with a metal component. In German Patent DE 10 2004 038 795, the production of photocatalytically active plastic surfaces by cold gas spraying is described. Japanese Patent JP2009066594 also discloses a method for cold gas spraying of photocatalytically active titanium dioxide that has been doped with nitrogen, carbon or sulphur, so that it is photocatalytically active in visible light. Cold gas spraying of titanium dioxide is also disclosed in Chinese Patent CN1443071.
In the article “Deposition of TiO2 Ceramic Particles on Cold Spray Process” by M. Yamada. et al. in DVB 264, 172-176, 2010, cold gas spraying of titanium dioxide is described in which mostly primary nanoparticles are used.
Cold as spraying of photocatalytically active titanium dioxide is described in the article “Formation of TiO2 photocatalyst through cold spraying” by C. -J. Li et al., IEEE Conference on Intelligent Transportation, ITSC Proceedings, 10 May 2004, pages 1-5. Such a method is also described by J. -O. Kliemann et al. in “Layer formation of cold-sprayed ceramic titanium dioxide layers on metal surfaces”, DVB 264, 90-85, 2010.
Cold gas spraying of photocatalytically active coatings is also described in EP 2 257 656. In this case, a matrix material with nanocrystalline titanium dioxide is used as the spray powder, and the photocatalytic activity is shifted into the visible spectrum by irradiating the processing site with UV or laser light while the cold gas spraying procedure is being carried out.